Medical sensor and technique for using the same

ABSTRACT

A medical sensor may be adapted to account for factors that cause irregularities in pulse oximetry measurements or other spectrophotemetric measurements. Sensors are provided with surface features that reduce the amount of outside light or shunted light that impinge the detecting elements of the sensor. The sensor is adapted to reduce the effect of outside light or shunted light on pulse oximetry measurements.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior U.S. application Ser. No.11/241,508, filed Sep. 29, 2005, the specification of which isincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and, moreparticularly, to sensors used for sensing physiological parameters of apatient.

2. Description of the Related Art

This section is intended to introduce the reader to various aspects ofart that may be related to certain aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In the field of medicine, doctors often desire to monitor certainphysiological characteristics of their patients. Accordingly, a widevariety of devices have been developed for monitoring many suchcharacteristics of a patient. Such devices provide doctors and otherhealthcare personnel with the information they need to provide the bestpossible healthcare for their patients. As a result, such monitoringdevices have become an indispensable part of modern medicine.

One technique for monitoring certain physiological characteristics of apatient is commonly referred to as pulse oximetry, and the devices builtbased upon pulse oximetry techniques are commonly referred to as pulseoximeters. Pulse oximetry measures various blood flow characteristics,such as the blood-oxygen saturation of hemoglobin in arterial blood, thevolume of individual blood pulsations supplying the tissue, and/or therate of blood pulsations corresponding to each heartbeat of a patient.In fact, the “pulse” in pulse oximetry refers to the time varying amountof arterial blood in the tissue during each cardiac cycle.

Pulse oximeters typically utilize a non-invasive sensor that emits lightinto a patient's tissue and that photoelectrically detects theabsorption and/or scattering of the transmitted light in such tissue.One or more of the above physiological characteristics may then becalculated based upon the amount of light absorbed or scattered. Morespecifically, the light passed through the tissue is typically selectedto be of one or more wavelengths that may be absorbed or scattered bythe blood in an amount related to the amount of a blood constituentpresent in the blood. The amount of light absorbed and/or scattered maythen be used to estimate the amount of the blood constituent in thetissue using various algorithms.

The pulse oximetry measurement depends in part on the assumption thatthe contribution of light that has not passed through a patient's tissueis negligible. However, outside light may leak into a sensor, causingdetection of light that is not related to the amount of bloodconstituent present in the blood. Additionally, light from a sensor'semitter may be reflected around the exterior of the tissue and mayimpinge the detector without traveling first through the tissue. Theselight sources may cause measurement variations that do not relate toamount of the blood constituent.

Some outside light infiltration into the sensor may be avoided byfitting the sensor snugly against the patient's tissue. However, such aconforming fit may be difficult to achieve over a range of patientphysiologies without adjustment or excessive attention on the part ofmedical personnel. Additionally, an overly tight fit may cause localexsanguination of the tissue around the sensor. Exsanguinated tissue,which is devoid of blood, may shunt the sensor light through the tissue,which may also result in increased measurement errors.

SUMMARY

Certain aspects commensurate in scope with the originally claimedinvention are set forth below. It should be understood that theseaspects are presented merely to provide the reader with a brief summaryof certain forms that the invention might take and that these aspectsare not intended to limit the scope of the invention. Indeed, theinvention may encompass a variety of aspects that may not be set forthbelow.

There is provided a sensor that includes: a sensor body; an emitterdisposed on the sensor body, wherein the emitter is adapted to transmitlight into tissue; a detector disposed on the sensor body, wherein thedetector is adapted to detect the light; and a patterned region disposedon a tissue-contacting surface of the sensor body between the emitterand the detector, the patterned region being configured to at leastabsorb, refract, redirect, or diffract the light.

There is also provided a pulse oximetry system that includes: a pulseoximetry monitor; and a pulse oximetry sensor adapted to be operativelycoupled to the monitor, the sensor comprising: a sensor body; an emitterdisposed on the sensor body, wherein the emitter is adapted to transmitlight into tissue; a detector disposed on the sensor body, wherein thedetector is adapted to detect the light; and a patterned region disposedon a tissue-contacting surface of the sensor body between the emitterand the detector, the patterned region being configured to at leastabsorb, refract, redirect, or diffract the light.

There is also provided a method that includes: delivering a first lightthrough a patient's tissue; detecting the first light delivered throughthe tissue; and redirecting a second light that does not propagatethrough the tissue away from the detector with a patterned region.

There is also provided a method that includes: providing a sensor body;providing an emitter adapted to transmit light into tissue; providing adetector adapted to detect the light; and providing a patterned regionon a tissue-contacting surface of the sensor body between the emitterand the detector, the patterned region being configured to at leastabsorb, refract, redirect, or diffract the light.

There is also provided a sensor that includes: a sensor body adapted tooperate in a transmission mode; an emitter disposed on the sensor body,wherein the emitter is adapted to deliver a first light into a tissue; adetector disposed on the sensor body, wherein the detector is adapted todetect the first light; and at least one protrusion disposed on atissue-contacting surface of the sensor body, wherein the at least oneprotrusion is adapted to reduce the amount of a second light impingingthe detector at an incident angle substantially not in-line with animaginary axis connecting the emitter and the detector.

There is also provided a pulse oximetry system that includes: a pulseoximetry monitor; and a pulse oximetry sensor adapted to be operativelycoupled to the monitor, the sensor comprising: a sensor body adapted tooperate in a transmission mode; an emitter disposed on the sensor body,wherein the emitter is adapted to deliver a first light into a tissue; adetector disposed on the sensor body, wherein the detector is adapted todetect the first light; and at least one protrusion disposed on atissue-contacting surface of the sensor body, wherein the at least oneprotrusion is adapted to reduce the amount of a second light impingingthe detector at an incident angle substantially not in-line with animaginary axis connecting the emitter and the detector.

There is also provided a method that includes: delivering a first lightthrough a patient's tissue; detecting the first light delivered throughthe tissue; and redirecting a second light that does not propagatethrough the tissue away from the detector with a protruding feature.

There is also provided a method that includes: providing atransmission-type sensor body; providing an emitter adapted to transmita first light into tissue; providing a detector adapted to detect thefirst light; providing at least one protrusion disposed on atissue-contacting surface of the sensor body, wherein the at least oneprotrusion is adapted to reduce the amount of a second light impingingthe detector at an incident angle substantially not in-line with animaginary axis connecting the emitter and the detector.

There is also provided a sensor that includes: a sensor body adapted tooperate in a reflectance mode; an emitter disposed on the sensor body,wherein the emitter is adapted to deliver a first light into a tissue; adetector disposed on the sensor body, wherein the detector is adapted todetect the first light; and at least one protrusion disposed on atissue-contacting surface of the sensor body, wherein the at least oneprotrusion is adapted to reduce the amount of a second light impingingthe detector at an incident angle substantially in-line with animaginary axis connecting the emitter and the detector.

There is also provided a pulse oximetry system that includes: a pulseoximetry monitor; and a pulse oximetry sensor adapted to be operativelycoupled to the monitor, the sensor comprising: a sensor body adapted tooperate in a reflectance mode; an emitter disposed on the sensor body,wherein the emitter is adapted to deliver a first light into a tissue; adetector disposed on the sensor body, wherein the detector is adapted todetect the first light; and at least one protrusion disposed on atissue-contacting surface of the sensor body, wherein the at least oneprotrusion is adapted to reduce the amount of a second light impingingthe detector at an incident angle substantially in-line with animaginary axis connecting the emitter and the detector.

There is also provided a method that includes: providing a sensor body;providing an emitter adapted to transmit a first light into tissue;providing a detector adapted to detect the first light; and providing atleast one protrusion adapted to reduce the amount of a second lightimpinging the detector disposed on a tissue-contacting surface of thesensor body, wherein the second light has an incident anglesubstantially in-line with an imaginary axis connecting the emitter andthe detector.

There is also provided a sensor that includes: a sensor body; an emitterdisposed on the sensor body, wherein the emitter is adapted to transmita light into tissue; a detector disposed on the sensor body, wherein thedetector is adapted to detect the light; and a light diffractingmaterial disposed on a tissue-contacting surface of the sensor body.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1A illustrates a perspective view of an embodiment of an exemplarybandage-style sensor with a patterned region in accordance with thepresent invention;

FIG. 1B illustrates a perspective view of the sensor of FIG. 1A with acheckerboard patterned region;

FIG. 1C illustrates a cross-sectional view of the sensor of FIG. 1Bapplied to a patient's digit;

FIG. 2 illustrates a cross-sectional view of an exemplary sensor withprotruding features applied to a patient's digit;

FIG. 3 illustrates a cross-sectional view of an exemplary reflectancesensor with protruding features;

FIG. 4A illustrates a perspective view of an embodiment of an exemplarybandage-style sensor with protruding features in a concentric pattern inaccordance with the present invention;

FIG. 4B illustrates a cross-sectional view of the sensor of FIG. 4Aapplied to a patient's forehead;

FIG. 5A illustrates a cross-sectional view of a region of an exemplarysensor with light absorbing protruding features in accordance with thepresent invention;

FIG. 5B illustrates a cross-sectional view of a region of an exemplarysensor with protruding features with a light absorbing coating inaccordance with the present invention;

FIG. 5C illustrates a cross-sectional view of a region of an exemplarysensor with light refracting protruding features with a light absorbingbacking in accordance with the present invention;

FIG. 5D illustrates a cross-sectional view of a region of an exemplarysensor with light diffracting protruding features in accordance with thepresent invention;

FIG. 6 illustrates exemplary protruding features for use with a sensorin accordance with the present invention;

FIG. 7 illustrates a cross-sectional view of an exemplary sensor with alight diffracting material in accordance with the present invention; and

FIG. 8 illustrates a pulse oximetry system coupled to a multi-parameterpatient monitor and a sensor according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

It is desirable to eliminate, reduce, or account for the possibleinfluence of light sources which may cause variability in pulse oximetrymeasurements. In accordance with the present techniques, pulse oximetrysensors are provided that reduce the amount of outside light thatimpinges the detecting elements of a sensor. Such sensors also reducethe amount of “shunted” light, i.e., light originating from lightemitting elements of the sensor that impinges the detecting elements ofa sensor without first passing through tissue. Sensors according to thepresent techniques incorporate surface features on or near thetissue-contacting surface of the sensor, such as protruding elements orprinted patterns, to influence the path of light from the undesiredlight sources and to direct such light away from the detecting elementsof the sensor. Such sensors may absorb, refract, or diffract the lightoriginating from these undesired light sources before such light canimpinge the detecting elements of the sensor.

Pulse oximetry sensors are typically placed on a patient in a locationthat is normally perfused with arterial blood to facilitate measurementof the desired blood characteristics, such as arterial oxygen saturationmeasurement (SpO₂). The most common sensor sites include a patient'sfingertips, toes, earlobes, or forehead. Regardless of the placement ofa sensor 10 used for pulse oximetry, the reliability of the pulseoximetry measurement is related to the accurate detection of transmittedlight that has passed through the perfused tissue and that has not beensupplemented by undesired light sources. Such supplementation and/ormodulation of the light transmitted by the sensor can cause variabilityin the resulting pulse oximetry measurements. The contribution ofambient or shunted light may adversely affect the measurement of theparticular blood constituent, such as SpO₂.

In many cases, light from undesired light sources propagates along anoptical path that is distinguishable from the optical path of theemitted light that is related to a blood constituent. In atransmission-type sensor, the sensor's emitter and detector lie onopposing sides of the tissue when the sensor is applied to a patient.The optical path of the signal light, which is light originating fromthe emitter that properly passes through perfused tissue, issubstantially in-line with an imaginary axis connecting the emitter andthe detector. For reflectance-type sensors, the optical path of theemitted signal light is somewhat more complicated, as the light firstenters the perfused tissue and then is scattered back to the detector.In both transmission-type and reflectance-type sensors, shunted lightand ambient light generally propagate at angles substantially off-axisfrom the optical path of the signal light.

The exemplary sensors discussed below have surface features that act todivert shunted or ambient light away from the light detecting elementsof a sensor. In certain embodiments, those features may be patterns ordesigns. More specifically, FIG. 1A illustrates a perspective view of anexemplary bandage-style sensor 10 having a generic patterned region 12disposed on a tissue-contacting surface 14 of the sensor body 16. As onewith skill in the art understands, the tissue-contacting surface 14 ofthe sensor body 16 may be actually touching a patient's tissue, or maybe almost touching the patient's tissue, depending on the closeness ofthe sensor's 10 fit. As depicted, the patterned region 12 is disposed inthe region between the emitter 18 and the detector 20. The patternedregion 12 may include a material that absorbs, refracts, or diffractslight. The sensor 10 may be applied to a patient's tissue with adhesivesbandages 11.

For example, FIG. 1B illustrates a perspective view of the sensor 10Ahaving a checkerboard pattern 22 disposed on a tissue-contacting surfaceof the sensor body. As depicted, the checkerboard is an alternatingpattern of a light absorbing material 23. The material surrounding theportions of light absorbing material 23 may be the material from whichthe sensor body 16 is constructed.

FIG. 1C depicts a cross-sectional view of the sensor 10A with acheckerboard pattern 22 applied to a patient's digit 24. The opticalpath of signal light originating from the emitter is substantiallyin-line with an imaginary axis 26 connecting the emitter 18 and thedetector 20. A small percentage of the light emitted by the emitter 18may not enter the perfused digit 24. Instead, this light may be shuntedaround the space between the digit 24 and the sensor body 16. Theshunted light, depicted by wavy arrow 27, impinges the light absorbingmaterial in the checkerboard pattern 22, which absorbs the light, thuspreventing it from reflecting around the gap between the sensor body 16and the digit 24 to impinge the detector 20. It should be understoodthat the gap between the sensor body 16 and the digit 24 may bemicroscopic in scale for a sensor body 16 that conforms closely to thedigit 24. Further, the gap may be discontinuous when interrupted bypoints where the sensor body 16 is touching the digit 24. Thecheckerboard pattern 22 reduces the overall reflectivity of the sensorbody 16 on the tissue-contacting surface 14, which may reduce the amountof shunted light that reaches the detector 20. The checkerboard pattern22, or other suitable pattern or design, may easily be applied to thesensor body 16 with inks or dyes, and is thus a low-cost modificationwhich may reduce measurement errors. In certain embodiments, thepatterned region 12 does not protrude from the sensor body 16. However,in other embodiments, as depicted in FIG. 1C, the checkerboard patternmay be laminated onto the sensor body 16 so that it protrudes slightlyfrom the sensor body 16.

A patterned region 12 may include a first material and a secondmaterial. The first material may be the material from which the sensorbody is constructed. The second material may be a light absorbing, lightrefracting, or light diffracting material, or a combination thereof. Thepatterned region 12 may include more than two materials, and may alsoinclude materials that are intermediate in their ability to absorb,refract, or diffract light. The patterned region 12 may also include ananti-reflective material. In certain embodiments, the patterned region12 may be a single material that is applied in varying intensity orconcentration to the sensor body. For example, a checkerboard pattern 22may be an alternating pattern of black ink and gray ink.

Additionally, the patterned region 12 may be a regular pattern, such asa checkerboard pattern 22, a concentric circles pattern, or a stripedpattern. The patterned region 12 may also be an irregular pattern thatis customized to provide redirection of light in specific areas of thesensor 10 which ambient or shunted light may be most likely to impinge.The patterned region 12 may be microscopic in scale, or it may bevisible to the unaided eye. In certain embodiments, it is envisionedthat the sensor body 16 is impregnated with the inks, dyes, or paintsused to make the patterned region 12.

Generally, it is envisioned that the patterned region 12 will cover atleast 1% of the surface area of the tissue-contacting surface 14 of asensor body 16. The tissue contacting surface 14 may include only thesensor body 16 or may also include the combined total tissue-contactingarea of the sensor body 16 and of the adhesive bandages 11. In certainembodiments, the patterned region 12 will cover 10-50% of the surfacearea of the tissue-contacting surface 14 of a sensor body 16. In otherembodiments, the patterned region may cover at least 75% of the surfacearea of a tissue-contacting surface 14 of a sensor body 16. Generally,it is contemplated that in addition to disposing a patterned regionbetween an emitter 18 and detector 20, it may be advantageous to disposea patterned region near any edges of the sensor 10A that may allowambient light to infiltrate into a sensor's 10 interior.

Furthermore, the patterned region 12 may have three-dimensionalprotruding surface features that function to divert ambient or shuntedlight away from the light detecting elements of the sensor. FIG. 2depicts a cross-sectional view of a transmission-type sensor 10B appliedto a patient digit 28. The sensor 10B has protruding surface features 30disposed on the tissue-contacting surface 32 of the sensor body 34. Theprotruding surface features 30 may be integrally formed or molded withthe sensor body 34, or they may be applied to the tissue-contactingsurface 32 of the sensor body 34 adhesively or otherwise. The protrudingsurface features 30 may be small-scale protruding features. Generally,small-scale protruding features as described herein are contemplated toprotrude less than about 0.001 mm from the tissue-contacting surface 32of the sensor body 34. In certain embodiments, the small-scaleprotruding features are not visible to the unaided eye. Alternatively,the protruding surface features 30 may be large-scale protrudingfeatures. Generally, large-scale protruding features as described hereinare clearly visible to the unaided eye, and they are contemplated toprotrude at least about 0.001 mm from the tissue-contacting surface 32of the sensor body 34. In certain embodiments, the large-scaleprotruding features protrude about 0.001 mm to about 1 mm from thetissue-contacting surface 32 of the sensor body 34. The protrudingfeatures may be sized and shaped to avoid substantially interfering witha suitably conforming sensor fit.

Turning to FIG. 2 in greater detail, the optical path of signal lightoriginating from the emitter is substantially in-line with an imaginaryaxis 36 connecting the emitter 40 and the detector 42. However, a smallpercentage of the light from the emitter, illustrated by wavy arrow 38,may not pass through the perfused tissue, but instead may be reflectedoff the surface of the digit 28 and shunted around the gap between thedigit 28 and the tissue-contacting surface 32 of the sensor body 34. Asthe shunted light, wavy arrow 38, propagates along its optical path, itimpinges the protruding features 30 on the tissue-contacting surface 32.The protruding features 30 change the optical path of the shunted light,reducing the amount of shunted light that impinges on the detector 42.

The sensor 10B may also reduce the contribution of outside light sourcesto pulse oximetry measurements. Ambient light, depicted as wavy arrow44, is shown leaking into the sensor 10B and impinging on the protrudingfeatures 30. The protruding features 30 reduce the amount of ambientlight that reaches the detector 42. As the protruding features 30 arenot in-line with the imaginary axis 36, the optical path of the lighttransmitted by the emitter 40 into the digit 28 is not substantiallyaffected by the protruding features 30. Hence, the contribution ofshunted light and ambient to the light received by the detector 42 isreduced, thus improving the signal to noise ratio.

In certain embodiments, it may be advantageous to use large-scaleprotruding features, as described above, to redirect light fromundesired light sources away from a detector. For example, when usingreflectance type sensors, it may be useful to block light that may shuntdirectly between the emitter and detector of such a sensor. FIG. 3illustrates a cross-sectional view of a reflectance-type sensor 10C withlarge-scale protruding features 46 adapted to block light from theemitter 48 that shunts directly to the detector 50 without first passingthrough perfused tissue. In certain embodiments, a light shunt betweenthe emitter 48 and the detector 50 may be addressed by placing one ormore large-scale protruding features 46 on the tissue-contacting surface52 of the sensor body 54 between the emitter 48 and the detector 50. Asthe emitted light, depicted by wavy arrow 56, strikes the side of thelarge-scale protruding features 46, it will be redirected away from thedetector 50. As depicted, the large-scale protruding features 46 areheterogeneous in size, and they are arranged such that the protrudingfeatures 46 closest to the detector 50 protrude the most from the sensorbody 54. In certain embodiments, at least one of the large-scale surfacefeatures 46 should protrude from the tissue-contacting surface 52 of thesensor body 54 at least as far as the detector 50 protrudes from thetissue-contacting surface 52 of the sensor body 54.

In another embodiment, shown in FIGS. 4A and 4B, large-scale protrudingfeatures may be arranged to form a pattern. FIG. 4A is a perspectiveview of a forehead sensor 10D with protruding features 56 arranged inconcentric circles that substantially encircle an emitter 58 and adetector 60. FIG. 4B is a cross-sectional view of the sensor 10D appliedto a patient's forehead. Such an arrangement of protruding features 56may be advantageous in forming a seal with the tissue 62, thus creatinga barrier against any ambient light or shunted light that may leak intothe sensor 10D. The ambient light, depicted by wavy arrows 64, impingesthe protruding features and is prevented from reaching the detector 60.The optical path of the signal light, depicted by wavy arrow 66, issubstantially unaffected by the protruding features 56.

In general, when shunted or ambient light impinges the protrudingfeatures, as described above, its optical path is altered and redirectedaway from the detector of a sensor 10. This may be accomplished in avariety of ways, as seen in FIGS. 5A-D, which depict cross-sectionalviews of exemplary sensor bodies with protruding features dispersed inthe patterned area 12. It should be understood that any of theprotruding features described below in FIGS. 5A-D may large-scale orsmall-scale, and they may be used alone or in combination with oneanother on any suitable sensor.

For example, as depicted in FIG. 5A, protruding features 68 may be madeof a light-absorbing material. The impinging light, depicted as wavyarrow 70, is refracted into the bulk of the light-absorbing materialwhere it is absorbed. In another embodiment, as seen in FIG. 5B,protruding features 72 may have a light-absorbing coating 74. Theimpinging light, depicted by wavy arrow 76, is absorbed as it contactsthe light-absorbing coating 74 of the protruding features 72. In anotherembodiment, shown in FIG. 5C, protruding features 78 may be made of asubstantially optically refractive material with an absorptive backing80. The light, depicted by wavy arrow 82, is refracted into therefractive material of the protruding features 78, and the refractedlight, depicted by wavy arrow 84, is absorbed by the absorptive backing80.

Alternatively, in another embodiment, shown in FIG. 5D, light fromundesired light sources may be directed away from the detector throughdiffraction. In such an embodiment, protruding features 86 may be madeof a diffracting material. For example, the diffracting material may bean interference grating material. As the impinging light, depicted bywavy arrow 88, impinges the protruding features 86, it is diffractedinto destructively interfering beams, depicted by wavy arrows 90 and 92,that substantially cancel each other out. It is contemplated that thediffracting material may be adapted to selectively interfere with atleast certain wavelengths. Thus, all or certain wavelengths of theimpinging light may be prevented from reaching a detector.

As described above, it may be advantageous to refract a beam of lightwhen it impinges a protruding feature as described herein. Ambient lightor shunted light may impinge a protruding feature after propagatingthrough air in the gap between the tissue and the sensor body.Alternatively, if the protruding feature is pressed tightly against thetissue, the light may travel through the cutaneous layer of the tissueto impinge the protruding feature. Light that impinges a protrudingfeature at an incident angle not normal, i.e., not 90 degrees, to theinterface of the protruding feature with the air or tissue and theprotruding feature will tend to be refracted. Thus, the protrudingfeatures may be shaped to promote light refraction. For example, asshown in FIG. 6, the protruding feature may have a generally sawtoothshape 94, which may be nonorthogonal to incident light leaking in. Inanother embodiment, a protruding feature 96 may have a complex profilein order to present a variety of possible interfaces to impinging light.Alternatively, a protruding feature 98 may have a curved profile topromote refraction. In certain embodiments, it is contemplated that theprotruding features may incorporate a patterned region, as describedherein, on their surfaces.

As described above in FIG. 5D, materials with light diffractingproperties may direct light from undesired light sources away from thedetecting elements of a sensor. FIG. 7 is a cross-sectional view of analternate embodiment of a sensor 10E with a light diffracting material100 disposed as a thin layer on a tissue-contacting surface 102 of thesensor body 104 applied to a patient's digit 106. The light diffractingmaterial 100 is disposed in a region between an emitter 108 and adetector 110. Light shunted by the emitter 108, depicted by wavy arrow112, impinges the light diffracting material 100. The light diffractingmaterial reduces the reflectivity of the shunted light by “smearing” thelight into multiple component wavelengths 114, many of which mayinterfere. The shunted light is thus prevented from reflecting aroundthe gap between the sensor body 104 and the digit 106 to impinge thedetector 110. It is contemplated that the diffracting material asdescribed here and in FIG. 5D may be customized to selectively reducecertain wavelengths. Specifically, the slit pattern of diffractiongrating may be optimized.

It should be appreciated that sensors as described herein may includelight absorbing materials, light refracting materials, light diffractingmaterials, or any combination thereof. For example, a tissue-contactingsurface, including all or part of any patterned regions or protrudingfeatures as described above, of a sensor body may be formed from, coatedwith, or impregnated with such materials. It should also be appreciatedthat, as discussed above, the sensor body may contain such materialsonly on a tissue-contacting surface, or, in alternate embodiments, thesensor body may be constructed entirely from such materials inappropriate regions as described herein.

It should also be appreciated that light absorbing materials may beadapted to absorb light at a particular wavelength. In certainembodiments, when light absorbing material is disposed between anemitter and a detector of a sensor, it may be advantageous to use lightabsorbing material that absorbs a wavelength emitted by the emitter inorder to absorb shunted light from the emitter. For example, a lightabsorbing material may absorb at least about 50% of one or morewavelengths of light from the emitter, or may absorb a range of 50% to95% of one or more wavelengths of light from the emitter. A lightabsorbing material may also absorb at least about 90% to at least 95% ofone or more wavelengths of visible light and near-infrared light. In aspecific embodiment, a pulse oximetry sensor may emit at least onewavelength of light in the wavelength range of 500 nm-1000 nm. Forexample, a sensor may emit light and wavelengths of 660 nm and 900 nm,which are wavelengths that may be absorbed by dark pigment. In otherembodiments, when the light absorbing material is disposed near theedges of a sensor in order to absorb ambient light, which includesmultiple wavelengths of light, it may be desirable to use an absorptivematerial that is adapted to absorb a broad range of wavelengths.Examples of light absorbing materials may include, but are not limitedto, black or dark pigment, black or dark woven fabric or cloth, andinfrared blockers.

Keeping in mind the preceding points, the exemplary sensor designsherein are provided as examples of sensors that increase the amount oflight collected by a sensor 10 that has passed through perfused tissuewhile reducing or eliminating outside light and/or shunted light. Itshould be appreciated that a sensor 10 according to the presentteachings may be adapted for use on any digit, and may also be adaptedfor use on a forehead, earlobe, or other sensor site. For example, asensor 10 may be a clip-style sensor, appropriate for a patient earlobeor digit. Alternatively, a sensor 10 may be a bandage-style orwrap-style sensor for use on a digit or forehead.

A sensor, illustrated generically as a sensor 10, may be used inconjunction with a pulse oximetry monitor 116, as illustrated in FIG. 8.It should be appreciated that the cable 118 of the sensor 10 may becoupled to the monitor 116 or it may be coupled to a transmission device(not shown) to facilitate wireless transmission between the sensor 10and the monitor 116. The monitor 116 may be any suitable pulse oximeter,such as those available from Nellcor Puritan Bennett Inc. Furthermore,to upgrade conventional pulse oximetry provided by the monitor 116 toprovide additional functions, the monitor 116 may be coupled to amulti-parameter patient monitor 120 via a cable 122 connected to asensor input port or via a cable 124 connected to a digitalcommunication port.

The sensor 10 includes an emitter 126 and a detector 128 that may be ofany suitable type. For example, the emitter 126 may be one or more lightemitting diodes adapted to transmit one or more wavelengths of light inthe red to infrared range, and the detector 128 may be a photodetectorselected to receive light in the range or ranges emitted from theemitter 126. For pulse oximetry applications using either transmissionor reflectance type sensors the oxygen saturation of the patient'sarterial blood may be determined using two or more wavelengths of light,most commonly red and near infrared wavelengths. Similarly, in otherapplications, a tissue water fraction (or other body fluid relatedmetric) or a concentration of one or more biochemical components in anaqueous environment may be measured using two or more wavelengths oflight, most commonly near infrared wavelengths between about 1,000 nm toabout 2,500 nm. It should be understood that, as used herein, the term“light” may refer to one or more of infrared, visible, ultraviolet, oreven X-ray electromagnetic radiation, and may also include anywavelength within the infrared, visible, ultraviolet, or X-ray spectra.

The emitter 126 and the detector 128 may be disposed on a sensor body130, which may be made of any suitable material, such as plastic,rubber, silicone, foam, woven material, or paper. Alternatively, theemitter 126 and the detector 128 may be remotely located and opticallycoupled to the sensor 10 using optical fibers. In the depictedembodiments, the sensor 10 is coupled to a cable 118 that is responsiblefor transmitting electrical and/or optical signals to and from theemitter 126 and detector 128 of the sensor 10. The cable 118 may bepermanently coupled to the sensor 10, or it may be removably coupled tothe sensor 10—the latter alternative being more useful and costefficient in situations where the sensor 10 is disposable.

The sensor 10 may be a “transmission type” sensor. Transmission typesensors include an emitter 126 and detector 128 that are typicallyplaced on opposing sides of the sensor site. If the sensor site is afingertip, for example, the sensor 10 is positioned over the patient'sfingertip such that the emitter 126 and detector 128 lie on either sideof the patient's nail bed. In other words, the sensor 10 is positionedso that the emitter 126 is located on the patient's fingernail and thedetector 128 is located 180° opposite the emitter 126 on the patient'sfinger pad. During operation, the emitter 126 shines one or morewavelengths of light through the patient's fingertip and the lightreceived by the detector 128 is processed to determine variousphysiological characteristics of the patient. In each of the embodimentsdiscussed herein, it should be understood that the locations of theemitter 126 and the detector 128 may be exchanged. For example, thedetector 128 may be located at the top of the finger and the emitter 126may be located underneath the finger. In either arrangement, the sensor10 will perform in substantially the same manner.

Reflectance type sensors generally operate under the same generalprinciples as transmittance type sensors. However, reflectance typesensors include an emitter 126 and detector 128 that are typicallyplaced on the same side of the sensor site. For example, a reflectancetype sensor may be placed on a patient's fingertip or forehead such thatthe emitter 126 and detector 128 lie side-by-side. Reflectance typesensors detect light photons that are scattered back to the detector128.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Indeed, the presenttechniques may not only be applied to measurements of blood oxygensaturation, but these techniques may also be utilized for themeasurement and/or analysis of other blood constituents using principlesof pulse oximetry. For example, using the same, different, or additionalwavelengths, the present techniques may be utilized for the measurementand/or analysis of carboxyhemoglobin, met-hemoglobin, total hemoglobin,intravascular dyes, and/or water content. Rather, the invention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A sensor comprising: a sensor body adapted to operate in atransmission mode; an emitter disposed on the sensor body, wherein theemitter is adapted to deliver a first light into a tissue; a detectordisposed on the sensor body, wherein the detector is adapted to detectthe first light; and at least one protrusion comprising a surfaceprotruding non-orthogonally from a tissue-contacting surface of thesensor body and comprising a patterned region disposed on a surface ofthe protrusion, and wherein the at least one protrusion is adapted toreduce the amount of a second light impinging the detector at anincident angle substantially not in-line with an imaginary axisconnecting the emitter and the detector.
 2. The sensor, as set forth inclaim 1, wherein the sensor comprises at least one of a pulse oximetrysensor or a sensor for measuring a water fraction.
 3. The sensor, as setforth in claim 1, wherein the emitter comprises at least one lightemitting diode.
 4. The sensor, as set forth in claim 1, wherein thedetector comprises at least one photodetector.
 5. The sensor, as setforth in claim 1, wherein the at least one protrusion protrudes lessthan about 0.001 mm from the tissue-contacting surface.
 6. The sensor,as set forth in claim 1, wherein the at least one protrusion comprisesmultiple protrusions.
 7. The sensor, as set forth in claim 1, whereinthe at least one protrusion comprises a light absorbing material.
 8. Thesensor, as set forth in claim 1, wherein the patterned region comprisesa checker board pattern, a striped pattern, or a concentric circlespattern.
 9. The sensor, as set forth in claim 1, wherein the patternedregion comprises alternating regions of a first material and a secondmaterial.
 10. The sensor, as set forth in claim 1, wherein the patternedregion comprises a material applied in varying intensity orconcentration to the protrusion.
 11. A pulse oximetry system comprising:a pulse oximetry monitor; and a pulse oximetry sensor adapted to beoperatively coupled to the monitor, the sensor comprising: a sensor bodyadapted to operate in transmission mode; an emitter disposed on thesensor body, wherein the emitter is adapted to deliver a first lightinto a tissue; a detector disposed on the sensor body, wherein thedetector is adapted to detect the first light; and at least oneprotrusion comprising a surface protruding non-orthogonally from atissue-contacting surface of the sensor body, wherein the at least oneprotrusion comprises a patterned region disposed on the surface of theprotrusion, wherein the at least one protrusion is adapted to reduce theamount of a second light impinging the detector at an incident anglesubstantially not in-line with an imaginary axis connecting the emitterand the detector.
 12. The pulse oximetry system, as set forth in claim11, wherein the sensor comprises a sensor for measuring a waterfraction.
 13. The pulse oximetry system, as set forth in claim 11,wherein the emitter comprises at least one light emitting diode.
 14. Thepulse oximetry system, as set forth in claim 11, wherein the detectorcomprises at least one photodetector.
 15. The pulse oximetry system, asset forth in claim 11, wherein the at least one protrusion protrudesless than about 0.001 mm from the tissue-contacting surface.
 16. Thepulse oximetry system, as set forth in claim 11, wherein the at leastone protrusion comprises multiple protrusions.
 17. The pulse oximetrysystem, as set forth in claim 11, wherein the at least one protrusioncomprises a light absorbing material.
 18. The system, as set forth inclaim 11, wherein the patterned region comprises a checker boardpattern, a striped pattern, or a concentric circles pattern.
 19. Thesystem, as set forth in claim 11, wherein the patterned region comprisesalternating regions of a first material and a second material.
 20. Thesystem, as set forth in claim 11, wherein the at least one protrusion issituated along an edge of the sensor body.
 21. The system, as set forthin claim 11, wherein the at least one protrusion substantially surroundsthe emitter or the detector.
 22. A method comprising: delivering a firstlight through a patient's tissue with a sensor adapted to operate intransmission mode; detecting the first light delivered through thetissue; and redirecting a second light that does not propagate throughthe tissue away from the detector with a protruding feature comprising apatterned region disposed on a surface of the protruding feature,wherein the surface of the protruding feature protrudes non-orthogonallyfrom a tissue-contacting surface of the sensor body.
 23. The method, asset forth in claim 22, wherein redirecting the second light comprisesabsorbing the second light.
 24. The method, as set forth in claim 22,wherein redirecting the second light comprises destructively interferingwith at least one wavelength of the second light.
 25. A methodcomprising: providing a transmission-type sensor body; providing anemitter adapted to transmit a first light into tissue; providing adetector adapted to detect the first light; providing at least oneprotrusion disposed on a tissue-contacting surface of the sensor body,wherein the at least one protrusion comprises a patterned regiondisposed on a surface of the protrusion, and wherein the at least oneprotrusion comprises a light diffracting material capable ofdestructively interfering with at least one wavelength of a second lightimpinging the detector at an incident angle substantially not in-linewith an imaginary axis connecting the emitter and the detector.
 26. Themethod, as set forth in claim 25, wherein the at least one protrusioncomprises a light absorbing material.
 27. The method, as set forth inclaim 25, wherein the at least one protrusion substantially surroundsthe emitter or the detector.
 28. A sensor comprising: a sensor bodyadapted to operate in a transmission mode; an emitter disposed on thesensor body, wherein the emitter is adapted to deliver a first lightinto a tissue; a detector disposed on the sensor body, wherein thedetector is adapted to detect the first light; and at least oneprotrusion comprising a patterned region disposed on a surface of theprotrusion, wherein the at least one protrusion is disposed on atissue-contacting surface of the sensor body, and wherein the at leastone protrusion comprises a light diffracting material, wherein the lightdiffracting material is adapted to destructively interfere with awavelength of light emitted by the emitter.
 29. The sensor, as set forthin claim 28, wherein the light diffracting material comprises aninterference grating material.
 30. A pulse oximetry system comprising: apulse oximetry monitor; and a pulse oximetry sensor adapted to beoperatively coupled to the monitor, the sensor comprising: a sensor bodyadapted to operate in transmission mode; an emitter disposed on thesensor body, wherein the emitter is adapted to deliver a first lightinto a tissue; a detector disposed on the sensor body, wherein thedetector is adapted to detect the first light; and at least oneprotrusion comprising a patterned region disposed on a surface of theprotrusion, wherein the at least one protrusion is disposed on atissue-contacting surface of the sensor body, and wherein the at leastone protrusion comprises a light diffracting material, wherein the lightdiffracting material is adapted to destructively interfere with awavelength of light emitted by the emitter.
 31. The pulse oximetrysystem, as set forth in claim 30, wherein the light diffracting materialcomprises an interference grating material.